When a conventional motor or generator, i.e. dynamo, is subjected to load, certain undesirable effects occur. For example, in D.C. or synchronous machines, armature reaction-leakage reactance is produced and in induction motors, rotor reactance is produced. These effects change both the magnitude and distribution of the flux crossing the air gap between the stator and rotor of such machines and adds vectorially to the main magnetic field flux, producing a resultant magnetic field flux which has a different distribution and intensity from the main magnetic field fluxes, causing phase and wave form distortions.
Thus, the electrical and magnetic neutral axis under load is shifted from the electrical and magnetic neutral axis at no load so that the effective magnetic field flux crossing the air gap is reduced and the induced e.m.f. in the armature or rotor conductors accordingly decreases, thus reducing the efficiency and performance characteristics of the rotating machine.
In our earlier patents 4,692,647 and 4,716,329, we have disclosed the provision of short-circuit ring coils and non-magnetic material to produce and position a counter flux for compensating distortions in the main flux in the air gap.
Referring to FIG. 10 which shows the construction of a dynamo according to our earlier patent 4,716,329 (FIG. 1'), the dynamo comprises a stator A constructed of magnetic material and having North and South poles N and S respectively, and a drum type rotor R secured to a shaft Sh which is rotatable about an axis O-O'. The stator A and rotor R form an air gap therebetween. A conventional main coil M is wound in external slots formed around the circumference of the rotor R. The main coil M is a drum winding, formed, for example, as a series winding around the periphery of the rotor. Also wound on the rotor are radial loop coils L which are separate from and do not interfere with the winding of the main coil M. The radial loop coils L are each of closed loop form and they extend in radial planes passing through axis O-O' at right angles to the main coil.
The rotor R includes a core C made of conventional magnetic materials such as silicon steel or low carbon steel. Interposed between the core C and shaft Sh is a cylindrical body D of nonmagnetic material such as stainless steel, aluminum, copper ally or the like. The body D of nonmagnetic material is fixed to the shaft Sh and to the rotor core C so that the entire rotor rotates around axis O-O'. The radial coils of closed loop form act to induce currents therein and produce flux which in combination with the nonmagnetic material of body D acts to produce a counterflux in the air gap to oppose the effects of leakage reactance and rotor reactance or armature reaction.